Closed fuse



July 16, 1940. M. J. JANSEN 2,208,187

CLOSED FUSE Filed May 12, 1937 Patented July 16, 1940 CLOSED FUSE Marinus Jacobus Jansen, Eindhoven, Netherlands, assignor, by mesne assignments, to Hartford National Bank and Trust Company, Hartford,

Qonn., as trustee Application May 12,

1937, Serial No. 142,267

In the Netherlands May 15, 1936 6 Claims.

'I'he casings of the usual closed fuses, for example for domestic use, generally have an inside diameter which is not less than half its length, .because when this diameter is smaller there is 5 great danger that the fuse will remain conductive after the fuse conductor has melted. This, of course, should bev avoided since melting of the fuse indicates an inadmissibly high current strength in the circuit. In addition there is often the danger of the casing exploding during fusion.

I have found that the above difficulty is probably due to the following. Due to the high temperature caused by the disruptive current, part of the fuse conductor volatilises at the moment of melting. This produces conductive particles which, due to the fact that the space in which the fuse conductor is arranged is closed, cannot escape, but deposit on the inner surface of the casing. Thus there is the risk that they may still constitute a conductive connection between the end contacts oi the fuse with the harmful result above indicated.

The object of the present invention is to overcome the above difficulties, and for this purpose the inner wall of the casing in which the fuse conductor is arranged is so proled, at least in the direction of its length, that after melting of the fuse conductor, the establishment of a conductive connection between the two end contacts is avoided. When the inner wall of the casing is profiled in this manner the disintegrated fuse conductor particles produced upon melting are not allowed to constitute a conductive layer.

harmful to the operation of the fuse. Thus, for example, the inner wall may be provided with protuberances. When these protuberances are small the wall has a roughened surface so that the fuse complies with the requisite conditions in a quite satisfactory manner. It has in addition been found that coating the inner wall oi' the hollow with a layer of moldable synthetic resin material in which grains of sand are baked gives excellent results. Particularly when the fuse is intended for high current .rengths it may be advisable that the material `from which the casing is made should have a small coefficient of expansion. Thus, the risk that the casing may explode at the moment of melting of the fuse conductor is substantially obviated.

The above-described fuses have the great advantage of being considerably smaller in cross section and thus less bulky than the usual ones. A casing according to the invention for a current strength of 6 amperes at a tension of 500 volts may have, for example in the case of the (Cl. 20D-131) usual length of about 40 mms., a diameter of from 2 to 3 mms. only, whereas the diameter ol.' the usual casing is about 21 mms.

It should be mentioned that open fuses are already known the diameter of which is less than half the length of the casing. Due to these fuses being open, it is possible for the particles disintegrated during melting of the fuse conductor to escape from the casing so that there is no risk that a conductive connection will be set up between the end contacts. The fact, however, that the hollow in which the fuse conductor is arranged is in open connection with vthe atmosphere allows, during' melting, for the production of an electric spark which can also pass out of the casing and entails the risk of lire. Fuses of thiskind can therefore be used only in very particular cases and are generally wholly unsuited for home systems.

If the fuse conductor of a fuse according to the invention is not soldered to the contact hoods but is clamped, any diiculties due to parts of the conductor becoming loose when solder is melted by the heat produced during melting of the conductor are avoided.

In order that the invention may be clearly understood and readily carried into eiect it will now be described more fully, by way of example, with reference to the accompanying drawing, in which:

lFigure 1 is a sectionized side view of a fuse according to the invention,

Fig. 2 is a sectionized side View of a fuse according to another embodiment of the invention, and

Fig. 3 is an enlarged view of a portion of the fuse of Fig. 2.y

Fig. 1 is a longitudinal section of a fuse according to the invention. The slight thickness relatively to the length of the cartridge can be clearly seen. Referring to this ilgure, reference numeral I indicates a tubular casing in which a fuse wire or conductor 2 is arranged. The ends of the fuse wire are connected by means oi solder 3a to contact hoods 3 which are pushed over the casing l. In this embodiment of thev invention, the inner surface of the casing I is provided with a number of annular protuberances 4 so that the object aimed at, in the present case the avoidance of the establishment of a conductive connection between the contact hoods upon melting of the wire 2, is achieved.

In the embodiment of the invention shown in Figure 2, the inner surface of the casing 5 is provided with a layer 6 which is made from a 2 moldable synthetic resin material with grains of sand baked in it. Asbetore. a fuse wire 1 is connected at its' ends to the contact hoods 8.

Referring to Fig. 3, part of the i'use shown in Fig. 2 is illustrated on a larger'scale. In this figure, the end 1a of the fuse wire 1 is, however, not connected to the hood. 8 by means of soldering material, but is clamped between a small plate I bearing on the casing 5 and the hood 8 so that the advantage described above is obtained.

What I claim is: 1. A closed fuse comprising a tubular casing of insulating material having anexternal width less than half its length, a contact member at eachend of said casing, a fuse element passing through the hollow space of the casing with its ends connected to said members, and means to prevent the establishment of a conductive connection between said members upon rupture of said element, said means comprising a coating of sand particles on the inner surface of the casing.

2. A closed fuse comprising a tubular casing of insulating material having an external width which is not more than one fth the length of the fuse, a contact member at each end of said casing, a fuse element-passing through the hollow space of the casingl with its ends connected to said members, and a coating of sand particles on the inner surface of said casing to prevent the establishment of a conductive connection between said members upon rupture of said element,

3. A closed fuse comprising a tubular casing of insulating' material and having an external Width not more than 8 mm., a contact member at each end of said casing, a fuse element passing through the hollow space of the casing with its ends connected to said members, and a coating of sand particles' on the inner surface oi said casing to prevent the establishment of a con-v ductive connection between said members upon rupture of said element.

4. A closed i'use comprising a tubular casing of insulating material havingv a width less than half its length, a contact member at each end of said casing, and a fuse element passing through the hollow of the casing with its ends connected to said members, the inner surface of said casing consisting of a molded mixture of sand and a' synthetic resin material to prevent the establishment of a conductive connection between said members upon rupture of said ele of a conductive connection between said mem-y bers upon rupture of said element.

6. A closed fuse comprising a tubular casing of insulating material and having an external width of not more than 8 mm., a'contact member at -each end of said casing, a fuse element passing through the hollow of the casing with' its ends connected to said members, and a coating of a. molded mixture of sand and a synthetic resin material on the inner surface of said casing to prevent the establishment of a conductive connection between said members upon rupture of saidl element.-

' MARINUS JACOBUS JANSEN. 

